Chorion (eggshell) protein genes isolated from Drosophila melanogaster will be mutated in vitro and reintroduced into the germ line by P element-mediated transformation. Strains containing single transferred genes at defined chromosomal sites will be isolated and the expression of the newly integrated gene in developing ovarian follicle cells studied. Specific changes in gene structure will be related to the ability of the chorion gene to undergo tissue and developmental stage specific amplification and transcription. The effect of the local chromosomal environment in diverse genomic regions on these properties will also be examined. Knowledge of the mechanisms which regulate and program gene replication and transcription during development is essential to understanding the etiology of birth defects, aging and acquired disease.